Biosphere is that part of the earth where life can exist. It is a narfqy layer around the surface of the earth. If you visualise the earth to be the size of an apple the biosphere would be as thick as its skin. The biosphere extends from the floor of the ocean some 11,000 metres below the surface of the earth to the top of the highest mountains, or about 9,000 metres above the sea level. Its most densely populated region is just above and below the sea level.Biosphere represents a highly integrated and interacting zone comprising of atmosphere (air), hydrosphere (water) and lithosphere (land) as you can see in Figure shown below.
Life inthe biosphere is abundant between 200 metres (660 feet) below the surface of the ocean and about 6,000 metres (20,000 feet) above sea level.
Biosphere is absent at extremes of the North and South poles, the highest mountains and the deepest oceans, since existing conditions there do not support life. Occasionally spores of fungi and bacteria do occur at great height beyond 9,000 metres, but they are not metabolically active, and hence represent only dormant life.The energy required for the life within the biosphere comes from the sun. The nutrients necessaj for living organisms come from air, water and soil and not from outside. The same chemicals are recycled over and over again for life to continue. Living organisms are not uniformly distributed throughout the biosphere. Only a few organisms live in the polar regions, while the tropical rain forests have an exceedingly rich diversity of plants and animals.